Using an USA iPh 6 in Taiwan?

I currently split my year between living in the US and Taiwan. I have an unlocked iPhone 3gs that works wonderfully in Taiwan. I spoke with Apple. They said the 6 is "internationally ready", but they can not guaranty me 100% that if I buy an "AT&T phone", I will be able to just install my Taiwan SIMS card and enjoy the same service I currently do with my unlocked 3gs.

Apple thinks the best choice would be for me to wait until the Official Unlocked iPhone 6 is released.
Has anyone switched SIMS cards / used their US iPhone 6 in Taiwan / Asia?